Abstract : It is well known that GPS C/A codes present cross correlation peak potentially causing false acquisitions. These cross-correlations peaks can in addition cause tracking errors and C/No degradation [1], [2], [3] and [4], not in traditional GPS tracking situations, but for applications where signals are received with low Doppler. There are several applications that can have low relative Doppler, and thus more frequent Doppler collision causing code cross-correlation interference : the first application occurs with the use of ranging signal broadcasted from geostationary satellites (SBAS systems) when two or more geostationary satellites are in common views of a fixed or low dynamic receiver (control station, reference station for differential positioning or any ground user with none or little motion), the second application occurs when ground pseudolites are used, with a receiver either on board a geostationary satellite or in a plane and on the ground as well. The findings described in this paper are part of the work performed by M3 Systems under a project initiated by the CNES (French Space Agency) which aims at studying the EGNOS RIMS performances. The work presented here aimed at: _Characterizing precisely these C/A codes interference tracking errors, _Identifying the exact factors driving the occurrence of these errors